System for controlling rolling mills

ABSTRACT

There is described a system for controlling the tensile force acting on a rolling material between individual sets of rollers of a continuous rolling mill. In order to carry out the continuous rolling operation with accuracy, the constants of transfer function of the tensionfree control loop is automatically corrected in accordance with variations in the rolling conditions such as dimension and shape of the steel material being worked, the rolling speed, the distance between individual sets of rollers and the like. Furthermore, the control includes a learning function.

United States Patent [1 3,863,478

Harada et al. Feb. 4, 1975 SYSTEM FOR CONTROLLING ROLLING MILLS [56]References Cited [75] Inventors: Toshio Harada; Shinichi Nakarnata,UNITED STATES PATENTS both of Kisarazu; Shiro Araki; Koei 3,188,8416/1965 Wallace 72/9 Nflkashima, bgth of Kitakyushu; 3,677,045 7/1972Arimura 61 a]. u 72/8 Hironori Kawasaki, Kimitsu; Kazuo g C erson23:12:: gfii g fi i t ggfg 3,7s2,|51 1/1974 Peterson 72/9 Kobe of JapanPrimary ExaminerMilton S. Mehr [731 Assignees: Nippon Steel Corporation;

Mitsubishi Electric Corporation, [57] ABSTRACT both of Tokyo, JapanThere is described a system for controlling the tensile 22 Ffled; Sept6, 1973 force acting on a rolling material between individual sets ofrollers of a continuous rolling mill. In order to [21] PP N05 394,844carry out the continuous rolling operation with accuracy. the constantsof transfer function of the tension- 0 Foreign Application p Data freecontrol loop is automatically corrected in accor- Se 1 6 I972 J3 an4188686 dance with variations in the rolling conditions such as 1972Japan 4.' 88687 dimension and shape of the steel material being p pworked, the rolling speed, the distance between indi- [52] U S Cl 72/672/9 vidual sets of rollers and the like. Furthermore, the [511 it C.'II"'I""f"'"'"""""'IIIIIIIIIIIIII m; m nnnnn' nnnnnnn n nnnnng fnnnnnn-[58] Field of Search 72/6-12, i9 15 Claims, 4 Drawing Figures lA lB lC/ROLLERS IROLLERS )ROLLERS LOAD LOAD 7 DETECTOR 7B DETECTORS 70 l 1 lDRIVE n DRIVE l 3A MOTOR 3B MOTOR 3c, ivicii s REVOLUTION 2A H 2BREV3LUTl0N 2c DETECTOR A "gggggtgg' 4 B ozrzcron I If I L SPEED SPEEDTENSION rgnsion CONTROL CONTROL I CONTROL I j l i r COMPUT ER PAIEHTEUsum 2 0F 5 ROLLERs ROLLERS ROLLERS IOA IOB IOC G 5 (5 DRIvE DRIvE 0 MM IMOTOR I MQTOR I HA B l IC i 2M 'rRAusPonIIIER 5 mansromzn 12": CURRENTCURRENT OIRRENT sOuRcE sOuRcE sOuRcE' A POWER POwER RHEOST T CONTROLCONTRQL FILTER 9/ FILTER SPEED E RI-IEOsTAT 2 MA SPEED CONTROL'T'LKSWITCH IGC MEMORY '24C 23B 23C "I SWITCH LS SPEED '78 385$8OLCONTROL SYSTEM FOR CONTROLLING ROLLING MILLS BACKGROUND OF THE INVENTIONField of the Invention The instant invention relates generally to acontrol system for a rolling mill, and more particularly to a system forcontrolling the tensile force acting on a rolling material betweenindividual sets of rollers of continuous rolling equipment.

In continuous rolling equipment where a rolling material extends overand is squeezed simultaneously by a number of rollers, it is necessaryto control the tensile force acting on the rolling material between theindividual rollers. In some cases, for example in continuous striprolling, a tensile force of a predetermined value is maintained in therolling direction in order to facilitate the compressive working of themetal. However, it is the usual practice in continuous rolling of steelsections to maintain the rolling material in tension free conditions toavoid defects or irregularities in the shape of the rolled material. Forthis purpose, conventional rolling mills are provided with a tensionpreventing control means of one form or another. With the conventionalcontrol devices of such nature, however, the same con stant of transferfunction is used for all the rolling conditions such as the dimension ofthe steel material to be rolled, the rolling speed, and the distancebetween the rollers, regardless of the particular shapes of the steelsections. In actuality, however, the rolling conditions do varydepending upon the particular schedule employed in the rollingoperation. In order to ensure an accurate rolling operation, it istherefore desirable to automatically correct the constant of transferfunction in response to variations in the actual rolling conditions.

With the foregoing in view, since the tension occurring between therollers during the rolling operation depends on the roller speeds whichin turn are influenced by the degree of complexity in the shape of thesteel material, rolling conditions of the steel material and variationsin the rolling loads, it has been found that, in order to control oreliminate the tension which would be imposed on the rolling materialbetween the individual rollers, the constant for a rolling mill drivingdevice, and more particularly, the constant for a tension controlcircuit should be determined as a function of the various rollingconditions including the dimension, shape, sectional area, rollingspeed, reduction ratio, forward slip ratio and backward slip ratio ofthe rolling material, thus eliminating the tension in the rolling direction.

It is therefore the primary object of the instant invention to provide asystem for automatically correcting the constant of the transferfunction in response to variations in rolling conditions to ensureaccurate control of the rolling mills.

The above and other objects, features and advantages of the instantinvention will be apparent from the following descriptions taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram of the control system according to the instantinvention;

FIG. 2 is a block diagram showing a tension control transfer functionloop;

FIG. 3 is a block diagram showing a system arrangement for rolling steelsections in accordance with the present invention; and

FIG. 4 is a block diagram of the system according to the instantinvention provided with a learning function.

DETAILED DESCRIPTION OF THE INVENTION Before proceeding with adescription of the preferred embodiments illustrated in the accompanyingdrawings, it is in order to discuss the principles for control' ling anddetermining the constant of transfer function for steel rolling undertension free conditions between the respective rollers of a continuoussteel section rolling mill.

The rolling schedule is generally determined by the reduction,temperature and load distribution characteristics of the particularrolling mill, and the rolling speed is determined in accordance with therolling schedule which meets a particular rolling mass flow. However,the tension is not always controlled appropriately due to difficulty inspeed control. It is therefore the usual practice to provide a tensionfree control system having a function transfer loop as shown in FIG. 2.However, there is herein described that the open loop transfer functionis varied, according to variations in the rolling conditions and to thedimension of the rolling material.

The mathematical relation of the tensile force or compressive force Twith the velocity V between two consecutive rollers or between a firstand second roller (I) wherein A is the cross-sectional area of thematerial, E is Youngs modulus, L is the distance between rollers, V,represents the velocity of the rolling material emerging from the firstroller and V represents the velocity of the rolling material enteringthe second roller. Hereinafter, the subscripts I and 2 indicate thefirst and second rollers, respectively. The relation between thevelocity of the rolling material and the angular ve locities N and N ofthe rollers is VR2= 2) NR2 wherein F. represents the forward slip rateof the rolling material emerging from the first roller while 5represents the backward slip rate of the material entering the secondroller. Experiments have shown that the forward and backward slip ratesof the rolling material vary linearly with the unit tension of thematerial. This is expressed as wherein a and B are constants, Frepresents a threshold or initial value of the forward slip ratio Frepresents a threshold or initial value of the backward slip rate A!ATM, and A represents the cross-sectional area of the steel material.If, in this instance, the angu lar roll velocities are varied by AN, andAN respectively, producing a tension T, the following equation isderived from the foregoing equations, (I) to (4).

wherein:

AT is the tension of the steel section between the two stands;

A is the sectional area of the steel section;

L is the distance between the two stands,

E is Young's modules a and [3 are constants N is the circumferentialvelocity of the first stand roll;

N is the circumferential velocity of the second stand roll;

5 is the Laplace operator;

F is the initial value of the forward slip ratio of the first stand;

( is the initial value of the backward slip ratio of the second stand;

F, is the forward slip ratio of the first stand;

5 is the backward slip ratio of the second stand; On the other hand, inthe tension control transfer loop shown in FIG. 2, the total transferfunction (1(3) including transfer function G ls) of the rolling mill andthe transfer function G (s) of the speed control device, if the constantof the high degree is disregarded, becomes wherein K represents atension gain, T a tension time constant. and T a loss time. Here, thetension gain is m U ANR2 m) Ril/( NR] "8' R2) A (W and the tension timeconstant T is TM B N wherein L represents the distance between rollersand E represents Youngs modulus Thus, it will be understood that thetension gain and the tension time constant of the total transferfunction GU) vary in accordance with the parameters 6, f, AM AN 0', ,3,L, E, A, N N Furthermore, if the transfer constant F(s) of the filtercircuit is considered as being fixed, optimum control of the tensioncontrol loop is obtained by setting the compensating transfer constantK(s) of the tension control loop with regard to the abovementionedvariables, as follows Km p+ l/ where K 7 X m/ m n) (lUl K, 5 X l/Km n(Ill wherein y and 6 are numerical constants, K is the proportionalconstant and K, is the integrated constant. Further, the tension timeconstant and the tension gain T and K respectively are expressed asfunctions wherein i represents an intermediate roller tension controlnumber, A represents a sectional area of the steel material in therolling mill, represents the constant. V represents a angular velocityof the roller. V represents the angular velocity of the first rollers inquestion, V represents the angular velocity of the second roller inquestion, K, representsfl L.E.A l, and K represents the ratio of theeffective coefficient of backward slip rate to that of forward sliprate.

Thus, K, of Equation (9) is derived from (ll) and l2) as follows lt /Tml/lCm fAMU fVU ml On the other hand, Kp of Equation (9) is derived fromEquations (l0), (ll) and ([2) as follows KP! 7 X n X m 'Y X n fl nunzvmm) (l5) From the foregoing, it is possible to calculate the setpoints Kand K, of the compensating transfer function K(s) for forming an optimumtension control loop.

A description will now be presented of a system of the instant inventionwhich operates on the principles discussed hereinabove Referring firstto FIG. 1, the reference characters 1A, [B and 1C designate pairedrollers of respective roller positions. Indicated at 2A. 2B and 2C arethe drive means for the rollers 1A, 1B and 1C, and at 3A, 3B and 3C aredetectors connected to the drive means 2A, 2B and 2C for detecting thenumber of revolutions of the rollers. There are shown at 4A, 4B and 4Cspeed control means for the aforementioned drive means 2A, 2B and 2C.Shown at 5A and 5B are tension preventing control means. Shown at 6 is atension computing control means such as a digital computer, and shown at7A to 7C are rolling load detecting means.

FIG. 2 shows a tension control transfer function loop, wherein the loopis formed by a transfer function F(.r) of the filter circuit, an optimumcompensating transfer constant K(s) of the tension control loop, atransfer function G,(s) of the speed control means 4A to 4C. and atransfer function (12(5') of the rolling mill. The loop produces currentvariation 8 resulting from the tension between two rollers. The currentvariation 8 produced by the tension between two rollers is fed to asumming point 9 at which a positive signal of the current in tensionfreerolling and a negative signal of the current variation 8 caused bytension are combined together so that tension control is carried out inaccordance with the result.

ln the instant invention, the setpoints K, and K for the respectivetension preventing control means are operated by the tension computingmeans 6 of FIG. I in accordance with Equations l2) and (I3) andutilizing other constants such as -y, 8, and T to produce a controloutput, before the rolling steel material enters the group of rollers ofthe continuous rolling mill. The respective tension preventing controlmeans 5A and 5B are operated in accordance with the control output whichis produced by the computer 6. When the steel material is passed througha first roller IA and then introduced into the next roller 18, it isdetected by the detector 78 whereupon the tension preventing controlmeans 5A carries out the optimum control after a time lag correspondingto the decreasing time of the impact speed. In a similar manner, whenthe steel material enters the roller 1C, the tension preventing controlmeans 58 is actuated. According to the speed correcting values which areissued from the control means 5A and 5B, the rolling speed is adjustedthrough the speed control means 48 and 4C. The tension computing controlunit 6 reads out the corrected speed to make the speed control in asubsequent operation more accurate.

It will be understood from the foregoing that the tension preventingcontrol unit can provide optimum control by way of the theoreticalcomputation which determines the tension control constant betweenrespective rollers, taking into consideration the rolling conditions andthe dimension of the steel material, instead of setting the control byexperience. The following description presented by way of example,applies the instant invention to the continuous rolling of double-Tsection steel.

In the continuous rolling of the double-T section steel, the rollingmaterial is maintained in a tension-free condition with no tensile norcompressive force acting thereon. In order to carry out the tension freerolling operation, it is the usual practice to employ the socalledcurrent memory system wherein as the rolling material is compressed at areference roller position, the current flowing through a drive motor ismemorized for comparison with the current flowing through the rollerdriving motor when the rolling material is introduced into a succeedingroller. The speed of the succeeding roller is controlled in accordancewith the difference therebetween. This conventional current memorysystem has difficulties in that, since it has a fixed control gain andemploys sampling or proportional control, a long operation time isrequired for controlling the respective rollers and therefore it becomesdifficult to obtain stabilized operation, particularly when the transfertime between the individual rollers is relatively short and/or there arerelatively large variations in the rolling speed or in the size of therolling material, due to the influences imposed when the succeedingrollers grip the rolling material.

As a result of various experiments and theoretical analysis carried outto elucidate the mechanism of producing tensile or compressive forcewhich gives rise to an unbalance in speed between two rollers, it hasbeen found that the relation between an unbalance in velocity and theforce between the two rollers is expressed by a time lag system of thefirst order.

In this connection, if the speed of the reference roller is constant,that is to say, with AN, =0, we obtain from Equation (5) and fromEquations (8) and (I6).

n L/E /l mi B ita/ ail] KM I zul az/ mi B NIH/NIH A If the rollingschedule is fixed, N /N a and ,6 become constant, so that That is tosay, the time constant T is substantially inversely proportional to theangular speed N, ofthe reference roller. Similarly, the tension gain K,of Equation I8) is from which it will be understood that ATs becomes astationary value which is proportional to a product of a percentagechange in speed or the amount of unbalancing in the speed and thesectional area of the rolling material.

With (19) and (20), Equations (l4) and 15) are rewritten as K I/Ng K aI/A [Ill Thus, in order to provide control in the tension having a timelag of the first order, the basic control system should preferablyinclude a control element having a transfer constant including aproportional constant and an integrated constant, these constantsvarying in accordance with the sectional area of the rolling materialand the angular speed of the reference rollers, whereby the timeconstant of the control will be suitable for the particular millcharacteristics, and will be controlled by the percentage in speedthereby maintaining the tension gain as a constant.

FIG. 3 shows a system for performing the control of the type discussedhereinabove, in the operation of continuous rolling mill for double-Tsteel sections. In FIG. 3, 10A to 10C are rollers corresponding to therollers 1A to IC of FIG. 1. The rollers are driven by DC motors 11A to11C, which in turn are powered by power sources 12A to I2C. The powersources are controlled by control units 13A to 13C. Current transformers 21A to ZIC are connected between the motors and the power source.Connected to the transformers are filters 15A to 15C and, memories 16Ato NBC. Indicated at 14A to 14C are speed rheostats, and 17A to 17Cindicated constant setting units. Indicated at 22A to 22C are 23A to 23Care switches, and indicated at 24A to 24C are adders.

This system controls the tension in the following manner. The armaturecurrent of the drive motor 11A which controls the first roller 10A in anarbitrary section of all the rollers, is detected by the currenttransformer 21A and fed to the memory 16A through the filter ISA and anormally closed contact of the switch 22A. After the following materialis gripped by the first rollers 10A and immediately before it isintroduced into the second rollers 105, the switch 22A is changed overto its other contact. The memory 16A memorizes and stores the drivemotor current of the first rollers (or the reference rollers) flowingimmediately before the rolling material is gripped by the secondrollers. The value of the current stored in the memory 16A and the valueof the actual current through the other contact of the switch 22A is fedto the adder 24A, and the difference between the two currents AI is fedto the constant setting unit 17A through the switch 23A which is closedwhen the rolling material is passing through the second rollers )8. Inresponse to a preset switch or a command signal from a computer, theconstant setting unit 17A deterines the proportional contact Kp and theintegrated constant K, in accordance with Equations (2i and (22) orEquations (l4) and (15 t, and produces a percentage change in speedsignal AS, as an output. The signal AS serves as a speed change commandsignal for the drive motor [1B of the second rollers, to adjust thesecond roller speed in accordance with the current variation Al untilthe tension AT becomes 0.

Immediately before the rolling material is gripped by the third rollers,the switch 228 is changed over to its other position and the armaturecurrent of the driving motor 118 for the second rollers which in thisinstance is the reference roller, is memorized by the memory I158. Theadder 243 gives a current variation Al to the constant setting unit l7Bwhich produces a percentage change in speed signal As which in turnserves as a speed change command signal for controlling the driven motor12C of the third rollers, until the current variation Al, and thus thetension AT becomes 0. in this manner, the tension between the successiverollers is controlled and maintained in a state.

With the above system, the speed change command signals AS, and A arealso applied to all of the successive rollers. The speed of each rollershould normally be in proportional relation when gripping the rollingmaterial. However, if the speeds of all the succeeding rollers arecorrected at the same time as the second rol ler, the amount of speedadjustment of each of the succeeding rollers may be reduced. In this wayas the rolling material reaches each of the succeeding rollers, theoperation time required for completing the control of that roller may beshortened to a significant amount.

FIG. 4 shows another embodiment of the instant invention which includesa learning function as an aid in controlling the tension. The controlunit containing the learning function is indicated by the block enclosedby line 26. This embodiment is essentially similar in operation as theone shown in FIG. 3 except for the control unit containing the learningfunction, and thus description of parts similar to that of FIG. 3 is notgiven here to avoid repetition. In FIG. 4, a computer 27 is employed forsetting the speed of the working rollers as well as the reduction value.Designated at 28 is a servomotor which is controlled by the computer 27by way of reversing switches 30 and 31. The servomotor 28 operates aslide arm of the speed setting unit 14B, There is shown at 29 a shaftencoder which indicates the position of the slide arm of the speedsetting device 14B and produces a positional signal in response theretoand applies this latter signal to the computer 27.

The operation of the learning control device 26 is as follows. Thepercentage change in speed signal AS, is fed to the computer 27, sothat. when the current devintion Al becomes 0 upon completion of thetension control, a signal S is supplied and the computer 27 memorizesthe change speed command signal A8,. A signal S is supplied when thetail end of the rolling material passes through the second rollers B,and the computer 27 then corrects the speed setting unit 145 accordingto the memorized value through the servo mechanisms 28 and 29. Thus,assuming the present position is expressed as P01 and the position afterlearning as Pnl, we can obtain the position of the slide arm of thespeed setting unit 148 as ll PM: 1 010 +2 ASi/IOO) Of course, thelearning term may be processed by means of the exponential averagemethod or other suitable methods. With the control according to theinvention, the roller speed setting for a subsequent rolling material iscorrected by means of the actual value obtained from the precedingrolling material, so that the computerized rolling mill control using amodel may be carried out far more accurately.

The percentage change in speed command signal AS, obtained from thesecond rollers IOB is used as a speed command signal for the thirdrollers and at the same time, controlling the succeeding rollers in thesame manner. The computer 27 is capable of providing learning controlalso for the speed setting unit of the third rollers, by using a similarservo mechanism.

The learning tension control method has been herein described inconnection with a current memory system, however, it will be appreciatedthat this method can be applied to systems other than the current memorysystem. In such a case, a speed deviation signal obtained from an outputof a reference speed generator may be used in place of the control inputASi.

With the system according to the invention, a sufficiently large controlgain is obtained in accordance with variations in the sectional area andthe speed of the rolling material in a continuous rolling operation forthe production of steel sections, so that tension control may be carriedout optimumly at all times with the result that it is possible to obtainsteel sections of high precision. The instant invention can also beapplied to continuous rolling of bar stocks, billet mills, rails, sheetpiles and the like, in the same manner as in the continuous rolling ofsteel sections as discussed hereinbefore.

Furthermore, the rolling mill control system of the present inventioncan be particularly advantageously applied to steel materials ofcomplicated shapes. Also, it may be used to control rolling millswithout the need of tension damping devices between the rollers.

A further advantage of the invention is that a signifi' cantly largegain is obtained through the learning control. The learning control maybe attained by directly adjusting the speed setting unit 148 inaccordance with the speed change command signals A8,, A5 and so on.However, this results in a far lower gain, as compared with the presentinvention employing a computer for the control of rolling mills.

What is claimed is:

l. A method for providing a zero tension in a steel section between atleast two stands of a continuous rolling mill, comprising the steps of:

a. detecting the speed of the steel section when it enters into thefirst stand and when it emerges from the second stand;

b. determining a plurality of parameters of rolling conditions includingat least the sectional area of the steel section between said first andsecond stands;

c. calculating a control constant based on said detected speeds and saidplurality of parameters, so that both the forward slip ratio andbackward slip ratio of the steel section may be linearly varied; and

d. modifying the speed of the steel section between said first andsecond stands in accordance with said control constant so as to maintainthe tension of the steel section therebetween substantially zero.

2. The method of claim 1 wherein said step of determining the pluralityof perameters includes determining the forward slip ratio and thebackward slip ratio of the steel section.

3. The method of claim 2 wherein said step of determining the pluralityof parameters further includes determining the dimension, shape, rollingspeed and reduction ratio of the steel section and distance betweenindividual stands.

4. The method of claim 3 wherein said step of calculating includescalculating the proportional gain and the integrated gain of a transferfunction, one of said gains being related to the sectional area of thesteel sec tion and the circumferential speed of a reference roll stand,to thereby select a time constant suitable for particular millcharacteristics.

5. The method of claim 4 wherein said step of calculating furtherincludes the step of obtaining a percentage change of speed signal.

6. The method of claim 1 wherein said rolling mill comprises a pluralityof stands and wherein said step of modifying the speed includessimultaneously applying a speed signal to all the stands subsequent tosaid first stand, for controlling the respective speeds thereof.

7. The method of claim I, further comprising the step of correcting thestand roll speed for a subsequent steel section by means of the actualvalue obtained from the preceeding steel section, so that thecomputerized rolling mill control using a model may be carried out farmore accurately.

8. The method of claim 1, further comprising the steps of:

e. memorizing the percentage speed change command signal when the tailend of the steel section is rolled in the second stand; and

f. correcting a speed setting unit for the second stand according to thememorized value through a servo mechanism.

9. A method for providing a zero tension in a steel section between atleast two stands ofa continuous rolling mill, comprising the steps of:

a. detecting the speed of the steel section when it enters into thefirst stand and when it emerges from the second stand;

b. using a plurality of parameters of rolling conditions including atleast the sectional area of the steel section between said first andsecond stands;

c. calculating a transfer function K(s) of the form Kl l (Ki/ where K,.is the proportional gain and K, is the integrated gain, and wherein:

where Cm, y and 8 are constants, V is the angular velocity of a roller,K represents f(L.E.A.), K represents the ratio of the effectivecoefficient of backward slip rate to that of forward slip rate and A isthe sec tional area of the steel section. and

d. modifying the speed of the steel section between said first andsecond stands in accordance with said transfer function so as tomaintain the tension of the steel section therebetween substantiallyzero.

10. The method of claim 9 and wherein for a particular rolling scheduleK as l/N X HA and K, l/A wherein N, is the circumferential velocity ofthe first roll stand.

11. Apparatus for providing a zero tension in a steel section between atleast two stands of a continuous rolling mill, comprising:

a. means for detecting the speed of the steel section when it entersinto the first stand and when it emerges from the second stand;

b. means for determining a plurality of parameters of rolling conditionsincluding at least the sectional area of the steel section between saidfirst and second stands;

c. means for calculating a control constant based upon said detectedspeeds and said plurality of parameters, so that both the forward slipratio and backward slip ratio of the steel section may be linearlyvaried;

d. means for controlling the speed of the steel section between saidfirst and second stands, and

e. means for applying said control constant to said controlling means inthe form of a percentage change of speed, so as to maintain the tensionof the steel section between the roll stands at substantially zero.

12. The apparatus of claim 11 and wherein said means for detectingfurther comprises drive means for rotating each of said sets of rollers,source means providing a current to said drive means, the speed at whicheach of said sets of rollers rotate being controlled by the amount ofcurrent to said drive means, memory means for receiving the amountcurrent controlling a given set of rollers at a time when the materialis passing through said given set of rollers, comparison means forreceiving the current controlling said given set of rollers at a timewhen the material has already entered the next successive set of rollersand comparing this last mentioned current with the current in saidmemory means and providing a current deviation signal.

13. The apparatus as in claim ll and wherein said control constantsinclude the values K w l/N X 1M and K; m wherein N, is the angularvelocity of the first roll stand, and A is the sectional area of thesteel section.

M. The system as in claim 11 and further comprising learning controlmeans for altering the operation of the sets of rollers in response tosaid speed correction signal.

15. The system as in claim 14 and wherein said learning control meanscomprises computing means receiving said percentage change in speedafter the speed of the sets of rollers is modified, speed setting meansfor setting the speed of each of said sets of rollers, and servomechanical means coupled to said speed setting means and under controlof said computing means, said computing means causing saidservomechanism means to control said speed controlling means to set thespeed of each set of rollers when the rolling material has passedtherethrough.

* it: n: a a

1. A method for providing a zero tension in a steel section between atleast two stands of a continuous rolling mill, comprising the steps of:a. detecting the speed of the steel section when it enters into thefirst stand and when it emerges from the second stand; b. determining aplurality of parameters of rolling conditions including at least thesectional area of the steel section between said first and secondstands; c. calculating a control constant based on said detected speedsand said plurality of parameters, so that both the forward slip ratioand backward slip ratio of the steel section may be linearly varied; andd. modifying the speed of the steel section between said first andsecond stands in accordance with said control constant so as to maintainthe tension of the steel section therebetween substantially zero.
 2. Themethod of claim 1 wherein said step of determining the plurality ofperameters includes determining the forward slip ratio and the backwardslip ratio of the steel section.
 3. The method of claim 2 wherein saidstep of determining the plurality of parameters further includesdetermining the dimension, shape, rolling speed and reduction ratio ofthe steel section and distance between individual stands.
 4. The methodof claim 3 wherein said step of calculating includes calculating theproportional gain and the integrated gain of a transfer function, one ofsaid gains being related to the sectional area of the steel section andthe circumferential speed of a reference roll stand, to thereby select atime constant suitable for particular mill characteristics.
 5. Themethod of claim 4 wherein said step of calculating further includes thestep of obtaining a percentage change of speed signal.
 6. The method ofclaim 1 wherein said rolling mill comprises a plurality of stands andwherein said step of modifying the speed includes simultaneouslyapplying a speed signal to all the stands subsequent to said firststand, for controlling the respective speeds thereof.
 7. The method ofclaim 1, further comprising the step of correcting the stand roll speedfor a subsequent steel section by means of the actual value obtainedfrom the preceeding steel section, so that the computerized rolling millcontrol using a model may be carried out far more accurately.
 8. Themethod of claim 1, further comprising the steps of: e. memorizing thepercentage speed change command signal when the tail end of the steelsection is rolled in the second stand; and f. correcting a speed settingunit for the second stand according to the memorized value through aservo mechanism.
 9. A method for providing a zero tension in a steelsection between at least two stands of a continuous rolling mill,comprising the steps of: a. detecting the speed of the steel sectionwhen it enters into the first stand and when it emerges from the secondstand; b. using a plurality of parameters of rolling conditionsincluding at least the sectional area of the steel section between saidfirst and second stands; c. calculating a transfer function K(s) of theform K(s) Kp + (KI/s) where Kp is the proportional gain and KI is theintegrated gain, and wherein: Kp gamma X KI X f(VR1, VR2, Kt1, Kt2) KI (delta /TD) X 1/(Cm X f(A) X f(VR)) where Cm, gamma And delta areconstants, VR is the angular velocity of a roller, Kt1 representsf(L.E.A.), Kt2 represents the ratio of the effective coefficient ofbackward slip rate to that of forward slip rate and A is the sectionalarea of the steel section, and d. modifying the speed of the steelsection between said first and second stands in accordance with saidtransfer function so as to maintain the tension of the steel sectiontherebetween substantially zero.
 10. The method of claim 9 and whereinfor a particular rolling schedule Kp varies as 1/NR1 X 1/A and KI variesas 1/A wherein NR1 is the circumferential velocity of the first rollstand.
 11. Apparatus for providing a zero tension in a steel sectionbetween at least two stands of a continuous rolling mill, comprising: a.means for detecting the speed of the steel section when it enters intothe first stand and when it emerges from the second stand; b. means fordetermining a plurality of parameters of rolling conditions including atleast the sectional area of the steel section between said first andsecond stands; c. means for calculating a control constant based uponsaid detected speeds and said plurality of parameters, so that both theforward slip ratio and backward slip ratio of the steel section may belinearly varied; d. means for controlling the speed of the steel sectionbetween said first and second stands, and e. means for applying saidcontrol constant to said controlling means in the form of a percentagechange of speed, so as to maintain the tension of the steel sectionbetween the roll stands at substantially zero.
 12. The apparatus ofclaim 11 and wherein said means for detecting further comprises drivemeans for rotating each of said sets of rollers, source means providinga current to said drive means, the speed at which each of said sets ofrollers rotate being controlled by the amount of current to said drivemeans, memory means for receiving the amount current controlling a givenset of rollers at a time when the material is passing through said givenset of rollers, comparison means for receiving the current controllingsaid given set of rollers at a time when the material has alreadyentered the next successive set of rollers and comparing this lastmentioned current with the current in said memory means and providing acurrent deviation signal.
 13. The apparatus as in claim 11 and whereinsaid control constants include the values Kp varies as 1/NR1 X 1/A andKI varies as 1/A wherein NR1 is the angular velocity of the first rollstand, and A is the sectional area of the steel section.
 14. The systemas in claim 11 and further comprising learning control means foraltering the operation of the sets of rollers in response to said speedcorrection signal.
 15. The system as in claim 14 and wherein saidlearning control means comprises computing means receiving saidpercentage change in speed after the speed of the sets of rollers ismodified, speed setting means for setting the speed of each of said setsof rollers, and servo mechanical means coupled to said speed settingmeans and under control of said computing means, said computing meanscausing said servomechanism means to control said speed controllingmeans to set the speed of each set of rollers when the rolling materialhas passed therethrough.